[0001] This invention relates to a method of producing a one-part silicone reinforced sealant
which is stable in the absence of moisture, but cures to an elastomer upon exposure
to moisture.
[0002] A method of economically producing a reinforced one-part silicone sealant which was
stable in the absence of moisture, but cured to an elastomer in the presence of moisture
was desired. Experience with the type of sealant based upon hydroxyl or alkoxy functional
polydiorganosiloxane, alkoxy functional crosslinker, and titanate catalyst revealed
that such sealants suffered in that as they shelf aged, they gradually lost the ability
to cure upon exposure to moisture.
[0003] A method was developed to make a sealant composition which had the desired physical
properties when cured and which had improved storage stability upon storage in the
absence of moisture.
[0004] Although there was no known published art which suggested how to solve the problem
of loss of cure upon storage of this type of silicone sealant, once the cause of the
problem was discovered other prior art became of interest.
[0005] United States Patent Number 3,122,522, issued February 25, 1964 to Brown and Hyde
discloses a siloxane composition, each molecule of which consists essentially of (1)
at least two units of the formula
[R′(OCH₂CH₂)
cO]
aR
b)SiZ(R₂)SiO
0.5
and units of the formula

where each
a has a value ranging from 2 to 3, each
b has a value ranging from 0 to 1, the sum of
a and
b in any unit (1) is no greater than 3, each
c has a value ranging from 1 to 2, each
d has a value ranging from 0 to 2, and Z is a divalent hydrocarbon radical of from
2 to 18 inclusive carbon atoms, Z being free of aliphatic unsaturation. Each molecule
of the silicone composition has an average of from 1.3 to 2 R groups per silicon atom
and there are at least 7 units of

per molecule.
[0006] United States Patent Numter 3,175,993, issued March 30, 1965 to Weyenberg discloses
a composition consisting essentially of the average formula

in which each R is free of aliphatic unsaturation, Z is a divalent hydrocarbon radical
free of aliphatic unsaturation,
y has a value of from 0 to 2 inclusive,
x has a value of at least 3, and
a has an average value of from 2 to 3 inclusive.
[0007] Both of the above references teach preparation of the siloxane by reacting siloxanes
containing -SiH groups with the appropriate silane containing a monovalent hydrocarbon
radical containing an aliphatic or cycloaliphatic group in the presence of a platinum
catalyst through the reaction of the -SiH and aliphatic C=C group. This reaction produces
the divalent Z radical. Alternatively, the C=C group can be on the siloxane and the
-SiH can be on the silane.
[0008] European Patent Application 123 935 A , published November 7, 1984 by Toten and Pines,
discloses an alkoxysilyl functional silicone including at least one functional group
of the formula

where
w is an integer of from 2 to about 20, useful as capable of imparting satisfactory
lubricity and other properties such as softness to a variety of textile fabrics.
[0009] European Patent Application 0110251, published June 6, 1984, discloses a process
for producing alkoxy-terminated polysiloxanes useful to produce room temperature
vulcanizing silicone rubber compositions. The process anhydrously reacts a silanol
or vinyl siloxane with a polyalkoxy crosslinking agent which is an alkoxy silane in
the presence of a platinum catalyst. This alkoxy-terminated polysiloxane can also
be mixed with treated filler and condensation catalyst. This application teaches that
an alkoxy-terminated polysiloxane having no silethylene linkage at the polymer terminal
silicon is equivalent to a polydiorganosiloxane that does contain a trialkoxysilethylene
terminal group.
[0010] There are many patents directed to the system of producing silicone sealants based
upon the use of alkoxy functional polymers, alkoxy functional crosslinkers, and titanate
catalysts. Representative of these is United States Patent Number 3,334,067, issued
August 1, 1967, to Weyenberg. Weyenberg discloses a method of making one component
room temperature curing siloxane rubber. His compositions are stable in the absence
of moisture, but cure upon exposure to moisture. The method comprises mixing in the
absence of moisture a hydroxyl endblocked siloxane polymer, a silane of the formula
R′Si(OR")₃ and a beta-dicarbonyl titanium compound.
[0011] In United States Patent Number 3,383,355, issued May 14, 1968, Cooper discloses polymers
having alkoxy groups bonded to terminal silicon atoms by reacting a hydroxylated organosiloxane
polymer with an alkoxy silane in the presence of a suitable catalyst. He discloses
that such functional diorganopolysiloxanes having from two to three alkoxy radicals
attached to each terminal silicon atom are curable in the presence of moisture and
a suitable hydrolysis and condensation catalyst to a rubbery material.
[0012] Smith et al., in United States Patent No. 3,856,839, issued December 24, 1974, disclose
alkanedioxy titanium chelates which catalyze the cure of a composition which also
contains methyltrimethoxysilane and a silanol chain-stopped polydiorganosiloxane fluid.
The particular chelated titanium compound is stated to be desirable because it does
not cause thickening during the manufacture of the composition as does the previously
known titanium compounds.
[0013] None of the disclosures in this background information is of any assistance in solving
the problem of how to improve the shelf life of silicone sealants that lose the ability
to cure upon long time storage in the absence of moisture, said sealants being catalyzed
with titanium compounds.
[0014] This invention is a process for producing a one-part silicone sealant which is stable
in the absence of moisture which contains an in situ treated reinforcing filler. A
diorganovinylsiloxy endblocked polydiorganosiloxane is combined with reinforcing
silica filler and silazane treating agent and heated to yield a reinforced base. The
base is then combined with a silane of the formula
H[SiR₂OSiR₂CH₂CH₂]
bSiR
a(OR")
3-a
in the presence of a platinum catalyst to give a trialkoxysilethylene ended polymer,
which is then combined with an alkoxy functional silane crosslinker and a titanium
catalyst, all mixing being without exposure to moisture, to yield the sealant which
is curable on exposure to moisture.
[0015] This invention relates to a method of producing a one-part silicone sealant stable
in the absence of moisture which cures on exposure to moisture having an in situ treated
filler comprising a method of producing a one-part silicone sealant stable in the
absence of moisture which cures on exposure to moisture having an in situ treated
filler comprising (A) mixing (1) 100 parts by weight of a diorganovinylsiloxy endblocked
polydiorganosiloxane where the viscosity of the siloxane is from 0.5 to 500 Pa·s at
25°C, (2) from 5 to 100 parts by weight of a reinforcing filler having a surface area
of from about 50 to 400 m²/g, and (3) from 0.5 to 4.0 parts by weight of a silazane
of the formula (RR"′MeSi)₂NH, where R is methyl, ethyl, propyl, phenyl, or trifluoropropyl,
R"′ is methyl or vinyl and where, if vinyl is present, the ratio of methyl to vinyl
is from 1:1 to 50:1, for each 10 parts of filler (2), (B) heating the mixture to a
temperature of 175°C with a nitrogen purge over the container to treat the filler,
(C) cooling, then adding (4) sufficient silane of the formula
H[SiR₂OSiR₂CH₂CH₂]
bSiR
a(OR")
3-a
where R is methyl, ethyl, propyl, phenyl or trifluoropropyl, R" is methyl or ethyl,
a is 0 or 1, and
b is 0 or 1, to give a ratio of 1 to 3 mols of silane per mol of vinyl radical in polydiorganosiloxane
(1), (5) from 1 to 50 parts by weight of platinum per million parts by weight of polydiorganosiloxane
(1) as platinum catalyst, then heating for from 30 to 60 minutes at a temperature
of from 65°C to 125°C, then (D) applying a vacuum and cooling to room temperature,
then (E) admixing in the absence of moisture, (6) from 3 to 15 parts by weight of
a crosslinker of the formula
R′
aSi(OR")
4-a
where R′ is methyl or phenyl, R" is methyl or ethyl, and
a is 0 or 1, and (7) from 0.2 to 2.0 parts by weight of a titanium catalyst, and (F)
storing the mixture in the absence of moisture.
[0016] The method of this invention is designed to produce, in the most economical manner,
a high strength silicone sealant that is stable in the absence of moisture for long
periods of time, but which cures rapidly when exposed to moisture. A reinforcing filler
is treated in situ to provide the potential high strength, then the reinforced polymer
is modified to change the ends of the polymer to a more stable form so that the final
sealant has a long storage life.
[0017] The diorganovinylsiloxy endblocked polydiorganosiloxane (1) is of the formula

where R is methyl, ethyl, propyl, phenyl, or trifluoropropyl. The value of
x is such that the viscosity of the polymer is from 0.5 to 500 Pa·s at 25°C. These
polymers are known materials which are manufactured by hydrolysis of the appropriate
diorganocyclosiloxanes in the presence of a hydrolysis catalyst such as potassium
hydroxide and an endblocking material such as divinyltetramethyldisiloxane.
[0018] The reinforcing filler (2) can be any of the commonly used fillers for silicone sealants
such as fume silica, precipitated silica, and diatomaceous earth, as long as they
have a surface area of from 50 to 400 m²/g so that they serve to reinforce the composition.
[0019] Ingredient (3) is used to treat the surface of the reinforcing filler (2) so that
the sealant does not creep upon aging. The silazane is of the formula (RR"′MeSi)₂NH
where R is methyl, ethyl, propyl, phenyl, or trifluoropropyl, R"′ is methyl or vinyl,
and where, if vinyl is present, the ratio of methyl to vinyl is from 1:1 to 50:1.
If a portion of the R"′ radicals are vinyl radicals, the treated, reinforcing filler
surface will also react with the silane (4) at the time of converting the polymer
(1) in step (C). The resulting sealant will then have a higher durometer and modulus
as the amount of crosslinking will be higher in the cured sealant. A preferred silazane
is hexamethyldisilazane. These silazane treating agents are well known in the art.
[0020] The preferred amount of silazane (3) is from 0.5 to 4.0 parts by weight per 10 parts
by weight of filler (2). The optimum amount of silazane (3) depends to some extent
upon the surface area of the filler (2) to be treated. Higher surface area fillers
need more of the silazane (3). Larger amounts can be used, but are not necessary.
[0021] The polymer (1) is converted to a polymer in which the end silica atoms are joined
by carbon atoms rather than by oxygen by reacting the reinforced polymer with silane
(4) of the formula
H[SiR₂OSiR₂CH₂CH₂]
bSiR
a(OR")
3-a
where R is methyl, ethyl, propyl, phenyl or trifluoropropyl, R" is methyl or ethyl,
a is 0 or 1, and
b is 0 or 1. Sufficient silane (4) is used to give a ratio of 1 to 3 mols of silane
per mol of vinyl radical in polydiorganosiloxane (1). When
b is 0 and
a is 0, the silane is of the formula HSi(OR")₃; when
b is 0 and
a is 1, the silane is of the formula HSiR′(OR")₂; when
b is 1 and
a is 0, the silane is of the formula HSiR₂OSiR₂CH₂CH₂Si(OR")₃; when
b is 1 and
a is 1, the silane is of the formula HSiR₂OSiR₂CH₂CH₂SiR(OR")₂.
[0022] When a vinyl endblocked polydiorganosiloxane (1) is reacted with a silane having
b equal to 0 and
a is 0, a polymer of the formula

is formed and when
b is 1 and
a is 0, a siloxane of the formula

is formed. When
a is 1, similar polymers are formed except the end group has the form -SiR(OR")₂ where
R is an organic radical selected from methyl, ethyl, propyl, phenyl, and trifluoropropyl,
and R" is methyl or ethyl, with methyl being most preferred. The radicals can be the
same or combinations of the above where at least 50 mol percent of the radicals are
methyl radicals.
[0023] The polymer of the formula (II) may be produced by reacting the appropriate vinyl
endblocked siloxane with the appropriate silane in the presence of a platinum catalyst
such as chloroplatinic acid at a temperature of from 30 to 150°C. Methods of making
these polymers are taught in United States Patent Number 3,175,993, issued March 30,
1965, to Weyenberg, which showsethods of manufacturing a polymer of formula (II).
[0024] The polymer of formula (III) is manufactured by reacting a vinyl endblocked polydiorganosiloxe
with an endcapping composition of the formula

where R and R" are as defined above, using a platinum catalyst to cause the materials
to react. R" is preferably a methyl radical. This endcapping composition is prepared
by reacting ViSi(OR")₃ with (R₂HSi)₂O in the presence of a platinum catalyst where
only one end of the disilane is reacted. This can be done combining 1 mol of the ViSi(OR")₃
with greater than 2 mols of the disiloxane. When this mixture is combined with a platinum
catalyst, there is a slightly exothermic reaction after a few minutes at room temperature.
The color changes from clear to light yellow. A by-product will be present consisting
of product produced by the reaction of ViSi(OR")₃ to both ends of the silane. This
by-product can be left in the material. At a 1 to 2 ratio, there is about 15 percent
by-product produced. If the ratio is changed to 1 to 4, the by-product drops to about
5 percent. The excess silane is then stripped from the product.
[0025] The preferred silane (4) is that in which
b is 1 and in which
a is 0. The ethylene link between the penultimate silicon atom and the end silicon
atom of the polymer, as in polymer III above, is thought to account for the improved
shelf life of the resulting sealant. It is also thought that the presence of two such
groups at the end of the polymer further improves the shelf life.
[0026] Ingredient (5) is a platinum catalyst of the type useful in the hydrosilation reaction.
Examples include platinum catalyst selected from those known to be useful in the hydrosilation
reaction. The platinum catalyst can range from platinum as deposited on carriers such
as silica gel or charcoal, to platinic acid, salts of platinum, chloroplatinic acid,
and compounds of platinum such as those described in United States Patents 3,419,593,
3,814,730, 3923,705, 4288,345, and 4,421,903 all of which show suitable platinum catalysts
and their methods of manufacture.
[0027] Ingredient (6) is a silane crosslinker of the formula
R′
aSi(OR")
4-a
where R′ is methyl or phenyl, R"is methyl or ethyl, and
a is 0 or 1. When
a is 0 or 1, the silane acts to crosslink the sealant. From 3 to 15 parts by weight
of the silane having
a either 1 or 2 or a mixture are needed to crosslink the sealant. In addition, silane
in which
a is 2 can be added to adjust the modulus of the sealant; the more of the chain extender
that is added, the lower the modulus and durometer. A methoxy endblocked polymer of
the formula
MeO(SiMe₂O)
kSiMe₂OMe,
where Me is methyl, and
k is from 1 to 10, is also useful as a chain extender. Up to about 10 parts by weight
of the chain extender are thought to be useful with about 5 parts being preferred.
The preferred crosslinker is methyltrimethoxysilane. The preferred chain extender
is methylphenyldimethoxysilane.
[0028] Ingredient (7) is a titanium catalyst such as titanium naphthenate, titanium esters
such as tetrabutyltitanate, tetra-2-ethylhexyltitanate, tetraphenyltitanate, triethanolaminetitanate,
organosiloxytitanium compounds such as those described in U.S. Patent No. 3,294,739,
and betadicarbonyl titanium compounds such as those described in U.S. Patent No.
3,334,067, both patents show titanium catalysts and methods of manufacture. Preferred
catalysts include tetrabutyltitanate, tetraisopropyltitanate, and bis-(acetyl-acetonyl)-diisopropyltitanate.
[0029] This invention is an improved method of producing a one-part silicone sealant which
is very stable in the absence of moisture, but cures rapidly when exposed to moisture.
The method is a very economical means of producing such a sealant. The method uses
materials which are produced in commercial quantities except for the silane (4). The
method uses a procedure which yields a surface treated filler in situ to further lower
the cost of production. The polydiorganosiloxane polymer is converted during the method
from a vinyl endblocked one to a methoxy ended one which has the last two silicon
atoms separated by an alkylene radical. This alkylene radical between the end silicon
atoms produces a sealant which is more shelf stable than one in which the alkylene
linkage is not present.
[0030] The first step in the method is (A) mixing of ingredients (1), (2), and (3) in a
heavy duty mixer which is capable of being heated and cooled and of being sealed from
the atmosphere with an inert gas purge or a vacuum being allied to the mixed contents.
Such mixers are those commonly used in the preparation of silicone elastomers. A preferred
procedure adds about one half of the polymer to the mixer, admixes the silazane, (3),
then adds the reinforcing filler (2) in increments, mixing each increment into the
polymer thoroughly before adding the next increment. The mixer is then heated to accelerate
the reaction between the filler surface and the silazane treating agent. A vacuum
is applied to the mixer contents to remove any moisture or other volatile material
and then the remainder of the polymer is admixed.
[0031] The polymer, containing the surface-treated filler, is then converted from a vinyl
endblocked polymer to an alkoxy endblocked polymer by adding silane (4) and platinum
catalyst to catalyze the hydrosilation reaction between the vinyl group on the polymer
and the hydrogen atom on the silane. This reaction is preferably done at a temperature
of from 65°C to 125°C for from 30 to 60 minutes. The reaction can be carried out at
lower temperatures, but more time then must be allowed for the reaction to go to completion.
The preferred silanes are those in which
a is 0 as the resulting trialkoxysilyl endblocked polymer is more reactive than the
alkyldialkoxy endblocked polymer obtained when
a is 1. It is also preferred that the silane be one in which
b is 1 because that silane has a lower vapor pressure and is less likely to be lost
in the conversion reaction. It is also felt that the silane in which
b is 1 is capable of giving a more shelf stable sealant. When
b is 0,
a is 0, and R" is methyl, the silane, trimethoxysilane, has a boiling point of about
84°C, so the reaction must be carried out at a low temperature or under pressure.
If carried out at low temperature, a longer period of time is necessary in order to
reach completion.
[0032] After the polymer is converted, any volatile products are removed by subjecting the
mixer contents to a vacuum. The mixer is then cooled without allowing any moisture
to come in contact with the contents. The mixer contents are then converted into a
sealant curable on exposure to moisture by adding crosslinker (6) and titanium catalyst
(7) and mixing to uniformity. The preferred crosslinker is methyltrimethoxysilane
because it is cheapest and most readily available. It is necessary to add about 6
parts of the crosslinker if it is desired to obtain a sealant having a shelf life
in the storage tube as the crosslinker acts as a scavenger and reacts with any moisture
or hydroxyl radicals which may be present in the mixture at the time the crosslinker
is added or which may get into the tube during the storage period. Theoretically,
it is not necessary to have any crosslinker present to cause a crosslinking of the
converted polymer (1) because it now has functional ends, but for practical products
the crosslinker (6) has been found necessary. If a lower modulus sealant is desired,
a silane (6) having
a equal to 2 can also be admixed at this time. The titanate catalyst is added to accelerate
the reaction between the alkoxy functional radicals and the moisture present during
curing to produce the crosslinked sealant. The useful range of titanium catalyst is
from 0.2 to 2.0 parts by weight. If less catalyst is used, the sealant will take longer
to cure, if more is used, the sealant will cure faster. More than 2.0 parts by weight
of catalyst can be used, but it serves no useful purpose.
[0033] The method of this invention yields a composition consisting essentially of (11)
100 parts by weight of a polydiorganosiloxane of the formula

where R is methyl, ethyl, propyl, phenyl, or trifluoropropyl, R" is methyl or ethyl,
a is 0 or 1,
b is 0 or 1,
c is from 1 to 6 and
x is such that the viscosity is from 8 to 500 Pa·s at 25°C, (12) from 5 to 100 parts
by weight of a surface-treated reinforcing filler having a surface area of from about
50 to 400 m²/g, (13) from 3 to 15 parts by weight of a crosslinker of the formula
R′
aSi(OR")
4-a
where R′ and R" are as defined above, (14) from 0 to 15 parts by weight of a chain
extender selected from the formula
PhMeSi(OMe)₂ or MeO(SiMe₂O)
kSiMe₂OMe
where Ph is phenyl, Me is methyl, and
k is from 1 to 10, and (15) from 0.2 to 2.0 parts by weight of a titanium catalyst.
[0034] The polydiorganosiloxane (11) is the result of the conversion of the polymer (1)
by the silane (4) in the method of the invention as in claim 1. The reinforcing filler
(2) has a treated surface because of the in situ treatment of filler by the silazane
(3). The method uses a platinum catalyst (5) which is present in the composition covered
by claim 4.
[0035] A similar conversion of polydiorganosiloxane polymer which is endblocked with dialkylhydrogensiloxy
radicals can be accomplished by converting with a material similar to silane (4) in
which the hydrogen atom is replaced by an alkenyl group, preferably vinyl. In other
words, the reactive groups are the same, they are just reversed in their location
in the respective reactants. The result would still be polydiorganosiloxane (11).
[0036] The sealant produced by the method of this invention is useful in filling cracks
and voids. The consistency of the composition before curing can be adjusted by choice
of the polymer (1) viscosity and the choice of amount and type of filler (2) to yield
a paste material which can be easily extruded from the storage container, for instance,
a common sealant tube. The moisture in the air will then convert the paste to an elastomer
through reaction of the polymer ends, crosslinker, and catalyst.
[0037] The method and composition of this invention can also contain the common ingredients
found in silicone sealants such as extending fillers and pigments. Extending fillers
include such as ground quartz and finely ground calcium carbonate. Pigments include
such as titanium dioxide, iron oxide, and carbon black. Because platinum is already
present in the composition, the addition of carbon black gives a sealant with enhanced
flame retardancy.
[0038] The following examples disclose preferred embodiments of the present invention and
should not be interpreted as limiting the scope of the invention which is properly
delineated in the accompanying claims. All parts and percentages are by weight unless
otherwise indicated.
EXAMPLE 1
[0039] A 1 qt. sigma blade heavy duty mixer was loaded with 150 g of dimethylvinylsiloxy
endblocked polydimethylsiloxane having a viscosity of about 10 Pa·s at 25°C and 6
g of water and mixed for 5 minutes. Then 24 g of hexamethyldi silazane treating agent
was added and mixed for 5 minutes, at which time 40 g of fume silica having a surface
area of about 250 m²/g was mixed in over a 15 minute period, then another 40 g of
the filler were added and mixed in. The mixer was then heated to 175°C and a vacuum
applied to the mixing chamber for 1 hour. Then 250 g of the polydimethylsiloxane was
added and mixed at the maintained temperature of 175°C and vacuum for one hour, at
which time the mixer was cooled to 125°C and 55 drops of chloroplatinic acid complex
of divinyltetramethyldisiloxane diluted with dimethylvinylsiloxy endblocked polydimethylsiloxane
to provide 0.7 weight percent platinum was added and mixed in for 5 minutes. The reinforeced
polymer was then converted by adding 14.34 g of HSiMe₂OMe₂SiCH₂CH₂Si(OMe)₃ and mixing
at 125°C for 45 minutes, then applying a vacuum while mixing for an additional 30
minutes, then cooling under vacuum for 30 minutes to yield a reinforced polymer having
the following structure

where
x was about 520. The viscosity of the polymer was about 10 Pa·s at 25°C.
[0040] This base was then converted to a sealant by mixing into 140 g portions of the base
the amounts of methyltrimethoxysilane crosslinker and tetrabutyltitanate catalyst
shown in Table I. This mixing was done in the absence of moisture and the mixtures
were placed in storage tubes which were sealed to keep out moisture.
[0041] After 1 week storage, samples of the sealants were extruded from the tubes and formed
into test sheets, which were allowed to cure on exposure to the atmosphere for one
week at room temperature. Test pieces were then cut from the cured sheets and tested
with the results shown in Table I. The durometer was tested according to ASTM D2240,
tensile strength and elongation according to ASTM D412, and tear strength, die B according
to ASTM D624.

EXAMPLE 2
[0042] A series of similar bases were prepared, except a dimethylvinylsiloxy endblocked
polydimethylsiloxane having a viscosity of about 30 Pa·s at 25°C was used in conjunction
with the amounts of ingredients shown in Table II. Two of the bases were then formulated
as above using the amounts of ingredients shown in Table II. The phenylmethyldimethoxysilane
is added as a chain extender to increase the elongation of the finished sealant. The
resultant sealants were packaged, stored and tested as in Example 1 with the results
shown in Table II.

EXAMPLE 3
[0043] Another series was prepared as in Example 2 except part of the polymer was replaced
with a polymer having a viscosity of about 0.4 Pa·s at 25°C as shown in Table III.
The resultant sealant was tested as above.

EXAMPLE 4
[0044] A series of compositions were prepared using different ratios of polydiorganosiloxane
(1) to silane (4).
[0045] Each composition was prepared by mixing 100 g of polymer (1), 30 g of filler, 6 g
of treating agent, and 1.5 g of water and preparing a base as in Example 1, then adding
14 drops of platinum catalyst and the amount of the silane (4) shown in Table IV and
converting the polymer as in Example 1. Each composition was then mixed with 8.0 g
of methyltrimethoxysilane and 0.64 g of tetrabutyltitanate and stored and tested
as in Example 1. The results are shown in Table IV, showing that at least 0.75 mol
of SiH from the silane (4) must be present for each mol of vinyl radical in the polymer
(1).
Example 5
[0046] The effect of the amount of crosslinker was evaluated. A base was prepared as is
Example 4 using 3.59 parts by weight of siloxane to convert the polymer. The base
was mixed with the amount of methyltrimethoxysilane shown in Table V and 0.6 part
by weight of the platinum catalyst. The resulting sealant was then aged and tested
as in Example 4 with the results shown in Table V.

1. A method of producing a one-part silicone sealant stable in the absence of moisture
which cures on exposure to moisture having an in situ treated filler comprising
(A) mixing
(1) 100 parts by weight of a diorganovinylsiloxy endblocked polydiorganosiloxane
where the viscosity of the siloxane is from 0.5 to 500 Pa·s at 25°C,
(2) from 5 to 100 parts by weight of a reinforcing filler having a surface area of
from about 50 to 400 m²/g, and
(3) from 0.5 to 4.0 parts by weight of a silazane of the formula (RR"′MeSi)₂NH, where
R is methyl, ethyl, propyl, phenyl, or trifluoropropyl, R"′ is methyl or vinyl, and
where, if vinyl is present, the ratio of methyl to vinyl is from 1:1 to 50:1, for
each 10 parts of filler (2),
(B) heating the mixture to a temperature of 175°C with a nitrogen purge over the container
to treat the filler,
(C) cooling, then adding
(4) sufficient silane of the formula
H[SiR₂OSiR₂CH₂CH₂]bSiRa(OR")3-a
where R is methyl,ethyl, propyl,phenyl or trifluoropropyl, R" is methyl or ethyl,
a is 0 or 1, and b is 0 or 1, to give a ratio of 1 to 3 mols of silane per mol of vinyl radical in polydiorganosiloxane
(1),
(5) from 1 to 50 parts by weight of platinum per million parts by weight of polydiorganosiloxane
(1) as platinum catalyst, then heating for from 30 to 60 minutes at a temperature
of from 65°C to 125°C, then
(D) applying a vacuum and cooling to room temperature, then
(E) admixing in the absence of moisture,
(6) from 3 to 15 parts by weight of a crosslinker of the formula
R′aSi(OR")4-a
where R′ is alkyl, vinyl or phenyl, R" is methyl or ethyl, and a is 0 or 1 and
(7) from 0.2 to 2.0 parts by weight of a titanium catalyst, and
(F) storing the mixture in the absence of moisture.
2. The method of claim 1 in which the silane of (4) is HMe₂SiOSi(Me₂)CH₂CH₂Si(OMe)₃.
3. The method of claim 1 in which there is also added at step (E),
(8) from 0 to 15 parts by weight of
PhMeSi(OMe)₂ or MeO(SiMe₂O)kSiMe₂OMe
where Ph is phenyl, Me is methyl, and k is from 1 to 10.
4. A composition consisting essentially of
(11) 100 parts by weight of a polydiorganosiloxane of the formula

where R is methyl, ethyl, propyl, phenyl, or trifluoropropyl, R" is methyl or ethyl,
a is 0 or 1, b is 0 or 1, c is from 1 to 6 and x is such that the viscosity is from 8 to 500 PA·s at 25°C,
(12) from 5 to 100 parts by weight of a surface-treated reinforcing filler having
a surface area of from about 50 to 400 m²/g,
(13) from 3 to 15 parts by weight of a crosslinker of the formula
R′aSi(OR")4-a
where R′ and R" are as defined above,
(14) from 0 to 15 parts by weight of a chain extender selected from the formula
PhMeSi(OMe)₂ or MeO(SiMe₂O)kSiMe₂OMe
where Ph is phenyl, Me is methyl, and k is from 1 to 10,and
(15) from 0.2 to 2.0 parts by weight of a titanium catalyst.
5. The composition of claim 4 in which b is 1.
6. The composition of claim 4 in which c is 1.
7. The composition of claim 4 in which carbon black is also present.